This application is based upon and claims the benefit of priority of Japanese Patent Application No. 2001-180388 filed on Jun. 14, 2001, the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an intake air control device, in particular, having an angular position detector capable of detecting an opening degree of a throttle valve for an internal combustion engine.
2. Description of Related Art
JP-A-8-254129 describes an intake air control device for an internal combustion engine as a prior art. This intake air control device has a throttle body provided with an intake air conduit leading to the internal combustion engine, a throttle valve mounted on a shaft rotatably held in the throttle body for opening and closing the intake air conduit, a valve gear fixed by means of a nut to an end of the shaft of the throttle valve, an intermediate speed reduction gear in mesh with the valve gear and a motor driving the intermediate speed reduction gear.
According to this conventional control device, a throttle position sensor is located at another end of the shaft on a side opposite to the valve gear. This construction makes an entire body of the control device larger. It is preferable that the throttle position sensor is a non-contact type sensor, in which a change of magnetic flux generated from a magnetic circuit constituted by a magnet and a yoke is detected by a non-contact type detecting element, and located at the end of the shaft on the same side as the valve gear. Further, in the conventional control device, the valve gear, which is formed in half-moon shape, has a notch portion coming in hitting contact with a stopper fixed to an installation base of the throttle body when the throttle valve is at a fully closed position.
However, the conventional control device has a drawback that, if the non-contact type sensor is employed, the valve gear interferes with the magnetic circuit so that magnetic flux generated from the magnetic circuit leaks to the valve gear since the valve gear is made of iron base magnetic metal.
Accordingly, the opening degree of the throttle valve or the angular position of the shaft can not be accurately detected. On the other hand, if the valve gear is made of thermoplastic resin, it is required to reinforce with metal material each local portion of the valve gear that is rigidly fixed to the shaft for installation or comes in hitting contact with the stopper. As a result, insert molding of many component parts including the magnet and the yoke becomes necessary when the valve gear is formed, causing higher manufacturing cost.
An object of the invention is to provide an intake air control device for an internal combustion engine in which a change of magnetic flux generated in a magnetic circuit in response to a change of an opening degree of a throttle valve is accurately detected with less number of component parts and at lower manufacturing cost.
To achieve the above object, in the intake air control device having a throttle body having an intake conduit to the internal combustion engine, a throttle valve having a shaft rotatably held in the throttle body for opening and closing the intake conduit, a rotary member rigidly fixed to the shaft for driving the shaft in response to an acceleration pedal so as to rotate the throttle valve and a non-contact type angular position detector having a magnetic flux generating member and a magnetic flux detecting element, the rotary member is made of non-magnetic metal, the magnetic flux generating member is attached to the rotary member so as to rotate together therewith and the magnetic flux detecting element is stationarily positioned to face the magnetic flux generating member with an air gap therebetween.
With the device mentioned above, the magnetic flux detecting element generates an electric signal in response to a change of magnetic flux applied thereto from the magnetic flux generating member so that an angular position of the shaft driven by the rotary member is detected. Since the rotary member is made of non-magnetic metal, the magnetic flux from the magnetic flux generating member is effectively applied to the magnetic flux detecting element without leaking to the rotary member so that the opening degree of the throttle valve is accurately detected.
Further, as the rotary member is made of non-magnetic metal, it is not necessary to reinforce with reinforcing material (such as other metal) a local portion of the rotary member that is rigidly fixed to the shaft.
It is preferable that the magnetic flux generating member is a permanent magnet and a yoke magnetized by the permanent magnet, both of which are rotatable together with the shaft and the rotary member.
Further, it is preferable that the rotary member has an outer protrusion integrally provided therewith and the throttle body has a stopper with which the outer protrusion comes in hitting contact for restricting further rotation of the rotary member when the throttle is fully closed. Since the rotary member is made of non-magnetic metal, it is not necessary to reinforce the outer protrusion that comes in hitting contact with the stopper. Accordingly, the control device can be manufactured with less number of component parts at lower cost.
Furthermore, it is preferable that the rotary member is formed in shape of a cup whose bottom wall is fixed to an end face of the shaft by staking or welding and whose inner circumferential wall is provided with the magnetic flux generating member. As the magnetic flux detecting element is accommodated inside the cap, an entire body of the non-contact type angular position detector becomes more compact.